Pre-impregnated (“pre-preg”) laminates of carbon fiber may be laid-up in a series of plies (tow/sections of carbon fiber tape) that are arranged into a complex shape and then cured into a composite part (e.g., a Carbon Fiber Reinforced Polymer (CFRP) part) having desired physical properties. Pre-preg laminates may be initially fabricated as a batch of dry carbon fibers that are oriented parallel with each other, which may then be impregnated with a thermoset resin. A resin may include, for example, a liquid suspension of multifunctional epoxy monomers which chemically react to form a solid polymer that binds carbon fibers together. Since the rate of polymerization may be particularly slow (e.g., operating on time scales that are unsuitable for mass fabrication), a catalyst is included within the resin to accelerate the rate of polymerization for the monomers. The pre-preg may then be laid-up into a desired form and cured.
However, it remains a complex process to balance the ratios of catalyst, monomer, and fiber. Since laminates may be fabricated as a series of layers that form a desired shape, it is desirable for resin to maintain sufficient adhesiveness (tack) at room temperature in order to ensure that plies adhere to each other, while still curing (engaging in accelerated polymerization) at an elevated temperature.
The curing kinetics of pre-preg laminates dictate that a balance be struck between work life and cure time. Work life corresponds with the amount of time that a ply exhibits tack (e.g., at room temperature) before curing. For pre-preg laminates that utilize a substantial amount of catalyst within the resin, work life is shortened and the resin rapidly becomes viscous, which is detrimental to layup processes. That is, although increased amounts of catalyst may provide highly accelerated cure times, they also may lead to an impractically short work life (“pot life”) for a laminate. In contrast, if not enough catalyst is utilized then cure time is extended, which reduces efficiency.
Certain pre-preg laminates may utilize a heat-activated catalyst within the resin in order to selectively trigger accelerated polymerization and thereby increase work life. However, heat-activated catalysts within the resin may fail to adequately penetrate between carbon fibers during the impregnation process, resulting in non-uniform distribution of resin (and therefore non-uniform cure characteristics) throughout the resulting pre-preg laminate, which is undesirable. In further embodiments, instead of a pre-preg laminate, a dry pre-form laminate may be utilized that comprises a batch of dry fibers that occupies a three dimensional (3D) shape.
For at least the reasons discussed above, it is desirable to seek out enhanced pre-preg laminates that uniformly exhibit desired properties of work life and cure time.